First of all agave nectar or syrup is a sweetener, like sugar, honey and molasses. It is a natural sweetener from the agave plant from which we also get taquilla. To turn agave plant into a sweetener, it takes a great deal of processing. Agave contains about 40% more calories per equal measure of sugar, so it isn’t a miracle diet substitution for sugar. The fact it is sweeter tasting than sugar means we may use less of it to achieve the same sweetness, but we won’t save calories.
The big advantage over sugar is agave has a better glycemic index than sugar and the other sweeteners mentioned here; meaning it doesn’t create a spike in blood sugar or immediately increase insulin when eaten. For this reason it is a dietary substitution for sugar for people with diabetes. Since agave syrup naturally has a sweeter impact than sugar, and if we use less of it, the calorie impact should be considered about equal.
In recipes, the exchange gets tricky for granulated sugar. Liquid measurements may need to be compensated for since it is a liquid. When substituting agave for honey or other liquid sweetener, it is recommended to use equal measures. People who eat vegan like to use agave instead of white sugar which may have been filtered through animal bone-based charcoal. It also subs nicely for honey if eating vegan.